ACTIVATION OF UNFERTILIZED STARFISH EGGS. 263 



gives rise to injurious conditions if it continues beyond a certain 

 time. For each temperature, in fact (from 30° to 38°), there is 

 a well-defined optimum duration of exposure which initiates 

 favorable development in all normal eggs ; also a briefer exposure 

 which results in simple membrane-formation followed by break- 

 down; and a more prolonged exposure which renders the egg 

 incapable of development. It is noteworthy that at each tem- 

 perature the ratios of the durations required for these several 

 effects are closely similar, — the optimum exposure being typically 

 from two to three times that required for simple membrane- 

 formation, and the maximum exposure (at which development 

 to a larval stage just fails) about one and a half times the 

 optimum.^ This indicates that some single process, involving 

 a critical change in the condition of the egg-protoplasm and 

 having a characteristically high temperature-coefificient, under- 

 lies and conditions all of these effects. This process does not 

 begin until a temperature of about 29° is reached, and proceeds 

 slowly at that temperature, taking approximately 30 minutes to 

 attain its completion. A rise of eight degrees accelerates it 

 some hundred times. Such facts appear to narrow the range of 

 possibilities very materially; they point clearly to some physical 

 change, — of structure, colloidal aggregation-state, viscosity, etc. 

 — rather than to one of a purely chemical kind, as constituting 

 the critical process underlying the activation of the egg. 



The experiments of the past summer have shown further that 

 exposure to weak fatty acid solutions produces in the egg effects 

 which are in all essential respects identical with those resulting 

 from exposure to the above temperatures. Starfish eggs placed 

 for one minute in sea-water containing n/260 butyric acid (2 c.c. 

 n/10 butyric acid phis 50 c.c. sea-water) all form fertilization- 

 membranes on return to normal sea-water; but if left without 

 further treatment the eggs typically fail to cleave and soon 

 break down without further development. Precisely the same 

 effect is produced by brief exposure to warm sea-water, e. g., 

 three or four minutes at 32°. In either case it is necessary, in 

 order to induce complete development of such eggs, to subject 

 them to some second or supplementary treatment, such as 



1 Cf. below, page 279. 



